1. Field of the Invention
The present invention relates to laser apparatus used as tools to process materials, and more particularly, to an optical system for laser apparatus for adjusting the peak power of the laser beam.
2. Background Art
Heretofore, lasers have been employed for selectively ablating material from a workpiece by the use of laser beam radiation and more particularly to ablating metal and/or dielectric workpieces by a pulse or pulses of laser beam radiation.
The selective removal of the material by laser radiation is well known. However, these techniques are not efficient and the processes cannot be controlled with sufficient precision. Processes known to the prior art characteristically provide undesirable side effects such as damage to the system illumination and projection optics by the peak power of the laser beam.
References describing the technique of laser ablation include U. S. Pat. No. 4,925,523 issued May 15, 1990 to Braren et al entitled "Enhancement of Ultraviolet Laser Ablation and Etching Organic Solids U.S. Pat. No. 4,752,668 issued Jan. 21, 1988 to Rosenfield et al entitled "System for Laser Removal of Excess Material from a Semiconductor Wafer" and U.S. Pat. No. 4,114,018 issued Sep. 12, 1978 to Von Allmen et al entitled "Method for Ablating Metal Workpieces with Laser Radiation".
In the present invention laser apparatus for material ablation is provided which employs techniques which use known optical structures such as beam splitters, polarizers, waveplates, mirrors and beam expanders. References that use these optical structures in combination for a variety of applications include U.S. Pat. No. 3,463,924 issued Dec. 16, 1966 to Culshaw et al entitled "Opposite Circularly-Polarized Optical Heterodyne Detection System. U.S. Pat. No. 3,464,026 issued Aug. 26, 1969 to Woodbury et al entitled "Laser Using Porro Prism End Reflectors". U.S. Pat. No. 3,700,334 issued Oct. 24, 1972 to Low et al entitled "Interferometer-Polarimeter". U.S. Pat. No. 3,881,823 issued May 6, 1975 to DeLang et al entitled "Apparatus for Measuring the Variation of an Optical Path Length with the Aid of an Interferometer". U.S. Pat. No. 4,059,759 issued Nov. 22, 1977 to Harney et al entitled "Passive and Active Pulse Stacking Scheme for Pulse Shaping". U.S. Pat. No. 4,180,324 issued Dec. 25, 1979 to Primboch entitled "Method and Apparatus for Measuring Deformation of a Workpiece Surface Responsive to Ultrasonic Energy". U.S. Pat. No. 4,188,122 issued Feb. 12, 1980 to Massie et al entitled "Interferometer". U.S. Pat. No. 4,224,096 issued Sep. 23, 1980 to Osborne entitled "Laser Sealing of Thermoplastic Material". U.S. Pat. No. 4,335,939 issued Jan. 22, 1982 to Stovell et al entitled "Optical Modulators and Apparatus Including Such Modulators".